The present invention relates to a system and a method for transmitting a paging message for an incoming call, and more particularly to a transmission system and a transmission method for mobile stations having intermittent receiving cycles different from each other.
As a paging message call transmission system, a mobile communication cellular system, and so on, have conventionally been used in order to transmit a paging message. In such a transmission system, a paging message for an incoming call to a mobile station in which power consumption has been reduced is received only by a predetermined slot for an incoming call therein, which results in so-called intermittent receiving. For this reason, it was necessary to transmit a particular paging slot for an incoming call with the timing of a paging message received while the mobile station was on standby. On the other hand, in a mobile station in which no reduction in power consumption was necessary, such as an on-vehicle mobile station, since all paging slots were received, a paging message was transmitted from a radio base station without using any particular paging slots.
In the conventional transmission system, when a paging message was received by the paging slot received by the mobile station, determination was made as to whether the message was for a call incoming to the present station or for a call incoming to another station based on the mobile station number contained in the paging message. If the paging message was discovered to be for the present station, then intermittent receiving was stopped and calling was carried out based on a call connecting procedure for call connection in order to be engaged in communication with the mobile station as a caller side. If the paging message is from another station, intermittent receiving can be maintained.
Next, an example of using a personal digital cellular communication system will be described. Referring to FIG. 5, there is shown a constitutional example of a common control channel which is transmitted from the radio base station of such a cellular communication system. A common control channel 500 transmitted from the radio base station (not shown in the drawing) time-division multiplexes a reporting channel 510 for carrying information to be reported, incoming call channels 520-1 to 520-3 for carrying paging messages, and individual cell control channels 530-1 to 530-4 for carrying call connection messages on the same frequency. Each of the channels for an incoming call is composed of a plurality of groups of slots for an incoming call so as to reduce the power consumption of the mobile station. For the division of the channels for an incoming call into groups, reference may be made to pp. 2 to 350 of the separate volume of the lecture papers of Electronic Information Communication Academy Spring National Convention held in March, 1990.
In such a communication system, upon having received information for an incoming call from the control station, the radio base station determines whether the information for the incoming call is for an intermittent receiving mobile station or a non-intermittent receiving mobile station. If the information is discovered to be for the intermittent receiving mobile station, the radio base station selects a paging slot to which the mobile station belongs. If the information is for the non-intermittent receiving mobile station, the base station selects a slot having the smaller number of paging messages on standby from a plurality of slots for incoming calls and transmits the messages for incoming call. On the other hand, during the standby period, the intermittent mobile station receives the paging slot to itself, the non-intermittent receiving mobile station receives all the paging slots and thereby all the paging messages can be received.
However, with the conventional transmission system, since a paging message transmission priority order was decided according to intermittent receiving cycles, the transmission of a paging message to the mobile station having a long intermittent receiving cycle was high in the priority order. Accordingly, when traffic was increased in the channel for an incoming call, a paging message for the mobile station having a short intermittent receiving cycle was not transmitted from the radio base station and it was impossible to call the terminal device having a short intermittent receiving cycle at all, which resulted in a reduction in transmission efficiency.